Roland Jet AP-7 issue

[stevenrb718]

Hey guys. I have a nice Roland Jet AP-7 that's giving me quite an issue. The "distortion" effect seems to work fine, but none of the positions have any phasing. Each set of 2 positions sound the same, I'm assuming because they're supposed to have a different phasing sound each time. The trim pot "phases" the effect when turned, but it only stays on that sound without moving itself. When plugging in a battery while connected, plugging in the audio jack, or quickly shorting out random items, the effect phases for a fraction of a second...almost like it's about to start phasing but just stops. First thought was caps, which all electrolytic caps were pulled and seem to be fine. The LM2902s were swapped with no changed, and the 30AY transistors were pulled, and none of them tested very out of the ordinary. The schematic is also very hard for me to read, so troubleshooting has been a pain. Anybody able to shed some light on it?

[Enzo]

The schematic is even harder for us to read since you didn't post it...

[stevenrb718]

The schematic is even harder for us to read since you didn't post it...

There it is.
Roland Jet Phaser AP-7 Service Manual.pdf

[Enzo]

Thanx.

Hey, I've seen worse.

[Mick Bailey]

My thought is that the oscillator isn't working. The actions; "When plugging in a battery while connected, plugging in the audio jack, or quickly shorting out random items, the effect phases for a fraction of a second...almost like it's about to start phasing but just stops." is maybe just the DC voltage shifting enough on the FET gates to give a momentary phasing sound, but once the DC stabilises the effect stops. Check if you have modulation at the switch (point 11 on the last schematic). Your DMM should be sufficient - even better if you can scope it.

When you say the electrolytics seem to be fine - what tests did you do?

[stevenrb718]

My thought is that the oscillator isn't working. The actions; "When plugging in a battery while connected, plugging in the audio jack, or quickly shorting out random items, the effect phases for a fraction of a second...almost like it's about to start phasing but just stops." is maybe just the DC voltage shifting enough on the FET gates to give a momentary phasing sound, but once the DC stabilises the effect stops. Check if you have modulation at the switch (point 11 on the last schematic). Your DMM should be sufficient - even better if you can scope it.

When you say the electrolytics seem to be fine - what tests did you do?

Are you referring to the wire point #11? That wire goes to 2 resistors and a lug of the Resonance pot. As for the aluminum caps, I pulled them from the circuit and plugged them into a tester. They seemed to all be within spec.

[Mick Bailey]

The point I refer to is the switch that selects between 56k and 220k resistors connecting to the opamps labelled 3 and 4. (the switch terminals are shown as 10,11,12) I don't know what your cap tester does, but if it just measures the value it may not give a true indication of the capacitor's condition.

[stevenrb718]

Ok, I see where you are. There looks to be at least 3 "11"s on the schematic, with the wire numbers also being different lol. That switch is the effect mode rotary. I measured voltage relative to ground at the switch wire and it's bouncing from about -3.7V to 3.7V. My tester also shows ESR and loss.

[Mick Bailey]

The oscillator looks to be working OK. Trace this through to the FET gates. The trim pot adjusts the DC bias on the FETs and if set incorrectly will reduce or prevent phasing, but you should still see the modulation voltage on the FETs, which act as voltage controlled resistors. Did you mark where the bias trimmer was set before you adjusted it? If not, set it halfway to begin with. Because the phaser passes audio and 'phases' when the bias trimmer is moved it could be down to a modulation issue. Your cap tester should be fine - high ESR is one of the problems with old electrolytics but is often overlooked and just the value measured.

[stevenrb718]

Ok, I think I'm on the right track now. That "11" point connects to a brown wire that goes off to the rotary Mode selector. I get continuity through different legs from the brown wire, but none go to any other location on the pcb or the pots. The drawing attached to the schematics is almost completely illegible by me, so this is going to be fun. I'll check voltage at all the other wired points, but it looks like I'm losing my pulse at the rotary switch.

[Mick Bailey]

Here's a better schematic; https://www.aronnelson.com/gallery/m...geViewsIndex=1 (But see the note on the switch replacements - these are not as per the original rotary switch)

[stevenrb718]

Yup, switch is broken. One of the pieces on the inside looks to be cracked. I managed to jump the line to the pcb and the phase returned. Now off to hunt down a replacement switch. Thanks for all the assistance.